Autoradiographic studies using 3H-thymidine indicate that new neurons are added to hyperstriatum ventralis, pars caudalis (HVc) of the adult canary brain. HVc is in the forebrain and is part of the song control system used in song learning. The new neurons are formed by division of ventricular zone cells, then migrate, differentiate and become connected to existing circuitry. Research planned for the next 5 years will describe the dynamics of neuronal recruitment in this system, the factors that control it, and the possibility that the new neurons replace older neurons. 3H-thymidine and autoradiography will continue to be used for this work, as well as silastic implants of steroid hormones, deafening by removal of both cochleas, and kainic acid lesions. The significance of neurogenesis and neuronal replacement in adult HVc will be studied by searching for temporal correlations between these phenomena and times of year during which adult canaries are particularly prone to learn new song syllables and forget old ones. The hypothesis tested here is that there is a correlation between the temporal occurrence of song learning, song forgetting and replacement of HVc neurons. The behavioral studies will involve song recording and sound-spectrographic analysis. Within this scenario our specific aims will be: 1. To measure the half-life of song perceptual and motor memories in adult male canaries, and the extent to which they are hormone dependent. 2. To determine the seasonal occurrence of neurogenesis and neuronal replacement in adult canaries, and their temporal relation to periods of song instability, forgetting and learning. 3. To determine to what extent, if any, hormones and experience influence neurogenesis and neuronal replacement in HVc. 4. To determine the survival curves of new HVc neurons, and the extent to which they may vary between different neuronal classes. 5. To determine how new HVc neurons orient during migration and find a place to work. 6. To determine to what extent neuronal recruitment occurs during the period from hatching to sexual maturity, so that patterns of recruitment (and replacement?) occurring at that time can be compared with those occurring in adulthood. 7. To interfere with neuronal recruitment and neuronal replacement in adult HVc to see how this affects memory retention and learning of new songs. An appreciaton of the occurrence and significance of neurogenesis and neuronal replacement in adult brain could have profound effects on neurological practice.